This invention relates generally to the surgical preparation of bones for a prosthetic joint replacement, and more particularly to the use of dry flowing gas to prepare a bone bed and thereby achieve enhanced fixation of a prosthesis to the bone.
In the field of orthopedic surgery, the standard surgical technique to prepare a bone for the implantation of prosthetic components presently consists of mechanically shaping a cavity in the bone, or sculpting a surface thereon, with a variety of manual and powered tools (drills, broaches, etc.). Then, the exposed bone bed is brushed and cleaned with a saline solution for lavage and irrigation. Finally, suction is applied to remove the debris. Surgical sponges are inserted into the cavity or against the bone surface to absorb excess fluids, and thrombin-soaked foam is occasionally used in an effort to slow the bleeding. Once the bone has been so prepared, the prosthetic component is introduced therein, and may be secured to the bone by various means, including friction or force-fit into the bone cavity, bone cement and/or pins or screws.
Prosthetic joint replacements are commonly secured to the adjacent bones with a material known generically as "bone cement." Presently, the bone cement typically used is polymethyl methacrylate. The availability of such cement in the U.S. since the late 1960's has enabled joint replacement surgery to become a routine orthopedic procedure. Despite its widespread success, however, a number of problems persist with cemented joint replacements, chief among them the significant potential for long-term implant loosening, a major clinical problem which often requires another operation. Loosening may occur at either the implant-cement interface or the cement-bone interface, but the latter is both more common and more difficult to forestall. Component loosening can result from inadequate bone bed preparation; interposed fluid or surgical debris prevent the cement from penetrating into the bone to achieve good contact and stable fixation.
As mentioned above, saline lavage is used to aid in washing away the debris generated by preparation of the bone surface, and to maintain irrigation for the operative field. In traditional surgical wound debridement procedures it is taught that prolonged drying is potentially harmful to tissues. The conventional wisdom of those skilled in the art of bone preparation for prosthesis fixation has been that it is important that those portions of a patient's body exposed in a surgical procedure (including the bones) be maintained in a moist or lubricated condition to avoid damage thereto or deterioration thereof.
The use of traditional liquid flushing lavage methods for cemented joint replacement surgery, however, has been shown to be less than ideal for preparation of the cancellous portions of an exposed bone bed. The bone cleaning capacity of these methods is limited to washing debris only from the exposed bone surface. Irrigating liquid which enters the interstices of the exposed bone actually prevents any significant cleaning beneath the bone surface, due to limited access of the irrigant to the deeper interstices. Debris cannot be removed from these interstices because the liquid cannot be easily flushed in and out of these deep, interconnected spaces. Since the irrigating liquid cannot be completely removed by surgical suction, cement penetration into the bone is also impeded: the cement cannot flow into the trabecular spaces which are filled with liquid, and on the trabeculae which the cement can reach, the moisture on the bony surfaces prevents true cement-bone contact. In an attempt to address the first of these problems and to improve the efficacy of lavage in the removal of bony debris, medullary fat and hematopoietic tissue, pulsatile lavage systems such as those described in U.S. Pat. No. 4,294,251 (Greenwald et al., issued Oct. 31, 1981) and U.S. Pat. No. 4,662,829 (Nehring, issued May 5, 1987) were developed. In these systems, the traditional flushing lavage is augmented by a pulsating delivery of the irrigating fluid, resulting in improved trabecular cleaning. This may be due to the ability of the intermittent flow to temporarily interrupt the formation of hydrostatic blockages in the bony pores.
Pulsatile lavage and improved cementing techniques such as pressurized cement injection have provided improvements in prosthetic fixation, but the cement-bone interface is still problematic. Bathing the bony surface with irrigating fluids washes away the natural blood clotting factors along with the surgical debris, which hampers the effort to achieve effective control over local bleeding. Ongoing bleeding can be a major problem in achieving good contact between cement and bone. Traditional surgical methods for controlling bleeding and achieving hemostasis, such as clamping the vessel or using electrocautery, are not applicable to bone. Current practice involves time-consuming methods of limited effectiveness: most commonly, repeated applications of thrombin-soaked foam are necessary to achieve even limited hemostasis. Thrombin powder is mixed with saline at surgery; small pieces of foam are soaked in this solution and applied to the bone cavities, removing them at intervals to see if bleeding has lessened and reapplying as necessary.
Blood and irrigation fluid not removed by suction lead to an unavoidable interposed fluid phase between the cement and the bone, preventing the intimate interdigitation desired for maximum interface strength. In addition, blood mixes into the cement and impedes uniform polymerization, thereby causing laminations which weaken the cement mantle by providing possible sites of local mechanical failure. Inadequate mechanical interdigitation significantly compromises prosthesis fixation in the case of the currently available bone cement, polymethyl methacrylate, because it is essentially a grouting agent, as opposed to an adhesive. Thus, successful skeletal fixation is entirely dependent upon the intimacy, integrity and extent of the mechanical interface between the cement and the cancellous portion of the bone. Blood between the cement and bone leads to radiolucent lines visible on x-rays of the joint, which then widen in association with progressive prosthetic loosening.
An improved cement-bone interface would also be useful in procedures which involve the generic surgical use of bone cement: i.e., procedures which do not necessarily involve implant fixation. Bone cement is also used for example, in the repair or filling of bony defects in cases such as pathologic fractures, where cement may be used to secure and augment an internal fixation device. Cement has been used as a spacer, after removal of a vertebral body, or occasionally after removal of an infected prosthesis, and cement has been used in neurosurgery to fill bony defects following procedures such as craniotomy. In these various other surgical uses of bone cement, enhancement of fixation of cement to bone could also be achieved by improving the bone preparation.
As mentioned above, in some circumstances, a prosthetic component is not cemented in place, but rather engaged with the bone by friction-fit or by some mechanical fastener (e.g., screw or pin). When a prosthetic component is affixed to a bone cavity without cement, it is also important to effectively control local bleeding, from the bone, in order to minimize the various medical risks of postoperative bleeding complications. Control of local bleeding from bone, not achievable by standard techniques for hemostasis, can also be important in other procedures not involving prosthetic implantation, such as in the removal of bone tumors.
As mentioned above, conventional surgical techniques involve moistening and irrigating the tissue during surgery to prevent drying. However, it is also conventional to "dry" the surface of the prepared bone by use of an absorbent packing such as a sponge. While such packing does absorb excess fluid from the bone bed surface and may even partially dry that surface by such absorption, it does not dry or remove fluids from the interstices of cancellous bone nor does it facilitate hemostasis within the bone structure. Thus, no one has previously attempted to dry both the surface and underlying interstices of a bone bed in the course of cleaning the bone bed and preparing it for acceptance of a prosthesis component. Of course, the use of blowing gas for clearing a surface or for drying is well known, and it has been known in the field of dentistry for quite some time to use compressed air in order to improve visualization. Saliva and irrigating fluids can be removed in this manner to aid the dentist's view of a constricted area such as a tooth.
Tofflemire U.S. Pat. No. 2,812,765 and Turner U.S. Pat. No. 3,208,145 illustrate devices which each combine into a single instrument three separate lines for providing irrigation, suction, and compressed gas: standard dental procedures which previously had required the use of three separate instruments. The Tofflemire patent also refers to the use of carbon dioxide gas as opposed to air. Carbon dioxide is widely used in other medical applications such as arthroscopy or gynecological laparoscopy (see, e.g., U.S. Pat. No. 4,735,603), and the safety of carbon dioxide use in the body is well documented.